1. Field of the Invention
The present invention relates to a servo writer for writing a servo signal for a tracking control of a tape memory medium such as a magnetic tape and a servo signal writing method.
2. Description of Related Art
In recent years, a memory capacity of a magnetic tape for, for example, data backup of a computer has been increased. The memory capacity of the magnetic tape has been increased with an extended tape by thinning a magnetic layer and makes total thickness of the magnetic tape smaller. A servo signal is written in advance in the magnetic tape. In a memory reproducing apparatus, a data track can be traced (servo controlled) by controlling a position of a read/write head by reading out the servo signal. This is disclosed in, for example, a first to seventh patent literatures listed below.                A first patent literature: claim 1, paragraphs 0013 to 0016, and FIG. 5 in Japanese Patent Laid-open Publication No. 2003-196810;        A second patent literature: paragraphs 0020 to 0025 and FIG. 2 in Japanese Patent Laid-open Publication No. 2005-332460;        A third patent literature: Specification of U.S. Pat. No. 6,970,312;        A fourth patent literature: Specification of US Patent Laid-open Publication No. 2005/0099718;        A fifth patent literature: Specification of US Patent Re-laid-open Publication No. 2005/0105967;        A sixth patent literature: Specification of US Patent Laid-open Publication No. 2005/0168869;        A seventh patent literature: Specification of US Patent Laid-open Publication No. 2005/0219734;        
In a magnetic tape in which the aforementioned servo control is conducted, accurate writing of a servo signal is important. Especially, a writing position from a reference edge of the magnetic tape must be accurate. A servo writer has been known, which writes a servo signal in a magnetic tape by making one side edge of the magnetic tape as a reference edge, while adjusting a positional variation of the reference edge in a tape width direction (for example, refer to the first patent literature).
In the servo writer described in the first patent literature, a positional variation in a tape width direction of a magnetic tape is adjusted based on a position of a reference edge of the magnetic tape, which is detected in an upstream of a writing head for writing a servo signal. Specifically, by inclining and moving the writing head in the tape width direction in response to a positional variation of a detected reference edge, thereby changing a tension of a magnetic tape in the tape width direction, a running position of the magnetic tape is displaced. Through the adjustment of the running position as described above, a servo signal can be written in an accurate position.
In addition, a servo writer which suppresses a positional variation in a tape width direction of a magnetic tape has been known (for example, refer to the second patent literature). In the servo writer described in the second patent literature, the positional variation in the tape width direction is suppressed by holding one edge of the magnetic tape from above with a plurality of arms and by sliding the other edge in contact with a contact portion.
However, the servo writer described in the first patent literature is one which adjusts a running position of a magnetic tape when it detected a positional variation in a tape width direction, and it does not suppress the positional variation itself in the tape width direction.
In addition, in the servo writer described in the second patent literature, a positional variation in a tape width direction is suppressed by holding both edges of a magnetic tape from both sides. However, if this method is applied to a recent thin magnetic tape, the magnetic tape may be easily damaged. If damages are produced, a sliding condition of the edge for the contact portion becomes wrong. As a result, since a running position of the magnetic tape is easily deviated, a servo signal could not be written accurately in the magnetic tape. Accordingly, PES (Position Error Signal), which is a servo quality, has been degraded.
It is, therefore, an object of the present invention to provide a servo writer which can write a servo signal accurately in a tape memory medium by suppressing a positional variation in a tape width direction of the tape memory medium.
It is another object of the present invention to provide a writing method of the servo signal.